Biomedical Engineering Reference
In-Depth Information
chitin/chitosan [169-171], gelatin, cellulose, hyaluronic acid
derivatives), proteins (soy, collagen, fibrin [11], silk) and a variety of
biofibers, such as lignocellulosic natural fibers [10, 172, 173]. Natural
polymers often posses highly organized structures and may contain
an extracellular substance, called ligand, which is necessary to bind
with cell receptors. However, they always contain various impurities,
which should be getting rid of prior use. As synthetic polymers can
be produced under the controlled conditions, they in general exhibit
predictable and reproducible mechanical and physical properties
such as tensile strength, elastic modulus and degradation rate.
Control of impurities is a further advantage of synthetic polymers.
Other authors differentiate between resorbable or biodegradable
(e.g., poly(α-hydroxyesters), polysaccharides and proteins) and
non-resorbable (e.g., PE, PP, PMMA and cellulose) polymers [60,
173]. Furthermore, polymeric materials can be broadly classified as
thermoplastics and thermosets. For example, HDPE and PEEK are
the examples of thermoplastics, while polydimethylsiloxane and
PMMA are the examples of thermosets [122]. The list of synthetic
biodegradable polymers used for biomedical application as scaffold
materials is available as Table 1 in Ref. [173], while further details
on polymers suitable for biomedical applications are available in
literature [122, 165, 174-183] where the interested readers are
referred. Good reviews on the synthesis of different biodegradable
polymers [184], as well as on the experimental trends in polymer
composites [185] are available elsewhere.
6.3.3
Inorganic Materials and Compounds
6.3.3.1 Metals
Titanium (Ti) is one of the best biocompatible metals and used most
widely as implant [16, 186, 187]. Besides, there are other metallic
implants made of pure Zr, Hf, V, Nb, Ta, Re [186], Ni, Fe, Cu [188-190],
Ag, stainless steels and various alloys [190] suitable for biomedical
application. Recent studies revealed even a greater biomedical
potential of porous metals [191-194]. The metallic implants provide
the necessary strength and toughness that are required in load-
bearing parts of the body and, due to these advantages, metals will
continue to play an important role as orthopedic biomaterials in the
future, even though there are concerns with regard to the release
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